1. Field of the Invention
The present invention relates in general to the field of computers and similar technologies, and in particular to managing path failure thresholds within computer system environments.
2. Description of the Related Art
Computing devices generate information. It is known in the art to store such information using a plurality of data storage devices disposed in an automated data storage system. An originating host computer may be in communication with a storage controller using a plurality of communication paths.
Using prior art methods, when a host computer detects a path failure during I/O to a storage device the host computer begins a path verification protocol. The host computer typically sends path verification commands to the device through each logical path recited in a device path mask. If the data returned in one of the path verification commands does not match the expected result, or the host path verification command times out, the host removes that logical path from the device path mask. At the completion of the path verification process, the device path mask may or may not still include the failed logical path.
The path verification process can become extremely time consuming if I/O failures are detected for multiple logical control units within the failure window of the several logical paths. As a result, a host computer can expend an inordinate amount of time and processing resources executing path verification commands rather than I/O commands. As a result, data storage system performance can be degraded.
In large, enterprise data processing system environments, a system 390 type host or other hosts that attach to a storage control unit are often use a channel path identifier (CHPid) operation to physically connect to a storage controller host adapter port directly to an input port of a switch. From the switch, the input port can be zoned to go to one or more output ports of the switch. The output port of a switch can be connected to a storage controller port. A host may have configured several CHPids to access different storage controller ports through direct or switch connection.
Through a physical connection between a CHPid and one or more input ports of a storage controller, a host establishes logical paths to communicate with a storage controller. A host may establish one or more logical paths per each logical control unit (LCU) of a storage controller. An LCU is the entity that contains a plurality of devices (e.g., up to 256 devices) to which a host accesses to perform input output (I/O) operations. To access a device from different logical paths of the same CHPid or several CHPids, it is known for a host to group up to eight logical paths into one path group.